A small grant application is made by a junior faculty member to analyze data previously collected on the effects of breathing an elevated but subclinical level of caron dioxide (CO2) -- similar to what might occur in self-contained breathing apparatuses (SCBAs). Proposed is research which will 1) further refine a methodology for quantifying the effects of environmental stressors and neurotoxins on human psychomotor performance and 2) analyze data from a CO2 experiment designed to provide information useful for recommending federal guidelines for the maximum allowable concentration of CO2 in SCBAs. In a 2x2x2x2x4 (Gas X Exercise X Stimulus Degradation X Stimulus-Response Compatibility X Time-on-Task) repeated measures design, six subjects each performed 20,000 trials on a serial four-choice reaction time task. Prior analyses examined only four of the five factors, omitting the exercise variable. Results showed main effects of each factor and an interaction of CO2 inhalation with stimulus-response compatibility which, according to the logic of the Additive Factors Method, suggests that breathing Co2 impairs central nervous system information process activity in the response selection stage of processing. Analyzing exercise as a fifth factor will indicate the effect of metabolic rate on information processing and describe its interaction with CO2 toxicity. Additional information obtained from the research will be especially useful to NIOSH for recommending 30CFR11 revisions.